Optically-based location system and method for determining a location at a structure

ABSTRACT

An optically based location system and method of determining a location at a structure include a lighting infrastructure having lights at a structure. Each light is configured to illuminate and to transmit a respective relative or absolute terrestrial position through modulation of emitted light. An optical receiver is configured to detect the lights, to demodulate the position of detected lights, and to determine from the detection a position of the receiver. The receiver can have a conventional optical detector for determining a two-dimensional position of the receiver relative to a detected light, or can have a three-dimensional spot collimating lens and charged couple device optical detector for determining a three-dimensional position of the receiver relative to a detected light. The receiver and lights can be synchronized for converting a delay time into a distance measurement to calculate a distance between a light and the receiver.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention lies in the field of electronic locationdetermination. The invention relates to an optically based locationsystem and a method for determining a location at a structure.

[0003] 2. Description of the Related Art

[0004] In the recent past, the Federal Communications Commission (FCC)has promulgated standards related to the Emergency-911 (“E-911”)initiative. This initiative has set the initial standards for acommunications system that, in the future, will precisely locate aparticular person or object. Particularly, the initiative relates toprecisely determining the location of a particular cellular telephone.As a result, location technologies have been developing rapidly. Therush to complete E-911, in particular, has compelled many cellularsystem designers to develop a scheme that will satisfy the locationrequirements set by the FCC.

[0005] Simultaneously, smaller-scale location opportunities, such aspersonal security and asset-management solutions, are beinginvestigated. The smaller-scale location technologies present many moreunsolved problems than the large-scale E-911 technology. One of the mostchallenging feats resides in the creation of technology that is able tolocate a device within or around structures. As set forth herein, theterms “structure” or “structures” mean any enclosure, including, but notlimited to, moveable enclosures, such as vehicles and robots. The termsdo not necessarily include only man-made structures, such as buildingsor cars, for example. An enclosure can have intermediate areas andwalls. The term “areas” as used herein is defined as any subset of anenclosed space within or a defined space around a structure. An “area”can mean, for example, a small room with four walls and a door, or itcan refer to a large room with many walls and doors and withintermediate cubicle-type half-walls. An “area” can also mean, forexample, places adjacent a vehicle.

[0006] Equipment that uses radio frequency (“RF”) signals to captureReceive Signal Strength (“RSS”), Time Difference of Arrival (“TDoA”), orAngle of Arrival (“AoA”) clues have limited location accuracy and oftenrequire an expensive supporting infrastructure. RF location schemes suchas RADAR, GPS, and LORAN have been used for years to locate peopleand/or objects outdoors. The realities of the indoor environment preventRF schemes from being employed indoors. Specifically, when RF propagatesin a building, the transmitted signal undergoes fading, dispersion, andinterference with delayed versions of itself—otherwise known in the artas multipath interference. Such signal impediments make it extremelydifficult to configure an indoor RF location system employing RSS, TDoA,or AoA for estimating a location of an object.

[0007] In most cases, existing optical in-building infrastructureincludes already-installed lights, such as incandescent bulbs,fluorescent lamps, and halogen bulbs, or even LED's or laser diodes.These definitions for the term “light” or “lights” are not exclusive. A“light” can refer to any device used for visible light illumination orinvisible light transmission, including, but not limited to, ultravioletand infrared. Other existing devices include sensors, RF transceivers,and processors that can perform position estimates based on signalstrength or some other ranging technology.

[0008] Various prior art devices and methods have used lighting forsending information in addition to providing illumination. The firstfour paragraphs of the background section of International PCTpublication WO 99/53732 to Leeb et al. detail the progression of suchdevices and methods over the past few decades. These paragraphs arehereby incorporated herein by reference. None of the cited patents,however, provide the features of the invention.

[0009] For example, WO 99/53732 discloses an apparatus for modulatingelectromagnetic radiation to transmit information from a visible-lightgenerating lamp such that human-perceptible flicker is eliminatedregardless of the information content. WO 99/53732 does not address ordisclose a system for locating an object in a building or using anoptical detector in a system for locating an object in a building.

[0010] Additionally, International PCT publication WO 00/30415 to Luptonet al. discloses an electronic communications network that uses indoorfixtures, emitting modulated visible light, as transmitters that do notgenerate human-perceptible flicker. Using warning indicators, i.e., aspeaker, the WO 00/30415 receiver indicates to a patient wearing thereceiver whether or not that patient is within an authorized area. TheWO 00/30415 photocell does not and cannot calculate its physicalposition with respect to a received light source based on the light itreceives from that source. Thus, it cannot calculate a distance from aparticular light source. The WO 00/30415 device also does not determinea relative or absolute position of a user from the light it receives.Further, WO 00/30415 only determines detectability within a given rangefrom a light source.

[0011] Finally, International PCT publication WO 99/53633 to Hovorka etal. discloses a communications network similar to WO 00/30415 having animproved bandwidth using a particular coding scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is an illustrative block diagram of the overallarchitecture according to the invention;

[0013]FIG. 2 is a perspective diagrammatic representation of a receiveraccording to the invention;

[0014]FIG. 3 is a perspective diagrammatic representation of the CCDarray of the receiver of FIG. 2;

[0015]FIG. 4 is a side view of the receiver of FIG. 2 with a partialcross-section of the lens;

[0016]FIG. 5 is a diagrammatic plan view of the CCD array of FIG. 3; and

[0017]FIG. 6 is a perspective diagrammatic representation of thereceiver of FIG. 2 in an example lighting infrastructure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] It is often forgotten that indoor environments were constructedto minimize audio and optical interference. Walls were erected and doorswere installed to keep in-building conversations private and tosubstantially prevent light from dispersing from one area to another. Atypical building, for example, is configured such that room A has onelight source and room B has another light source. Thus, the lightemitting from each respective source (e.g., the transmitted signal)cannot interfere with light emitting from another source. On the otherhand, if RF sources (transmitters) are used, multiple signalsoriginating from one area can and do interfere with each other and alsowith signals originating from other areas, including areas behind walls.When RF sources are used with in-building location detection systems,the interference skews a location sought to be estimated.

[0019] Instead of applying RF signals for determining location, thepresent invention uses optical signal technology in a unique way todetermine the location of an object at a structure using an existinglighting infrastructure within or around that structure. The presentinvention utilizes optical technology to keep the location-determiningsignals from interfering with each other and uses the particularfeatures of indoor environments to enhance the reliability ofdetermining a location of an object within a structure. The system andmethod of the present invention adds value to the existinginfrastructure by providing a position reference to a location map thatis created by the devices in the infrastructure. For a lightinginfrastructure, for example, each light can have a relative positiondefined with respect to a fixed position, such as an entrance to thebuilding. Alternatively or additionally, the example can be extended toprovide an absolute terrestrial position reference to the location mapcreated by the infrastructure. If the absolute terrestrial location ofthe entrance, for example, is defined, each light can have a relativeposition defined with respect to that absolute location and, therefore,an absolute position of that light can be determined. Alternatively,each light can have its own absolute terrestrial position as thereference.

[0020] As set forth herein, the terms “absolute terrestrial position” or“absolute position” mean a three-dimensional position relative to apredetermined coordinate system, for example, the coordinate system ofthe Earth, including positions on the Earth's surface, below the Earth'ssurface, and above the Earth's surface. Thus, an example absoluteterrestrial position could include latitude, longitude, and heightabove/below sea level. Another example could include an X-Y-Z positionwith respect to the center of the Earth. Another example could include acountry, state, city, address, and height above/below sea level. Thosehaving skill in the art can derive further equivalent examples.

[0021] Most location solutions have to combat the maladies ofin-building environments. In contrast, the invention exploitsin-building isolation properties and existing in-building transmissioninfrastructures, and components of those infrastructures, to provide aunique and robust indoor location solution that has not heretoforeexisted.

[0022] The present invention employs an optically enabled locationsystem that utilizes a building's existing indoor lightinginfrastructure and conventional optical receivers. The invention alsocan employ a unique three-dimensional (“3-D”) optical detector(receiver) that determines its own position relative to a light source,also called an illumination element. Particularly, the 3-D receiver“sees” a given light and determines a position relative to that lightsource using, in particular, a location vector. The invention furtherdetermines the identity of that given light source and, when the lightsource is identified, determines the light source's relative positionwith respect to a fixed point or the light's absolute location withrespect to the Earth. Given the relative position of the receiver fromthe light source and the light source's absolute position, for example,an absolute position of the receiver can then be determined with a greatdegree of accuracy. Thus, the invention presents a location system thatovercomes problems associated with RF-based location systems. Theinvention side-steps RF-signal impediment issues by employing a mediathat is not as susceptible to the aforementioned channel impediments.

[0023] The optical transmitters (light sources) and receivers of theinvention provide location information to the location devices operatingindoors. The receiver used in the system and method of the inventiondetermines the receiver's own relative or absolute position with thehelp of only one transmitting device. Most existing location systemsneed at least three, and, preferably, four, transmitting devices tocalculate a two-dimensional (“2-D”) position. One embodiment of thereceiver used in the invention is unique because it determines its own3-D relative or absolute position using only one transmitting device.The 3-D receiver employed by the invention, however, utilizes a 2-D AoAscheme in conjunction with RSS clues to calculate its position from onlyone transmitting device. The receiver extracts RSS, TDOA, and 2-D AoAclues from at least one light having an optical transmitter to estimatethe location of the transmitting light source and to determine thereceiver's own position based on a priori knowledge of the location ofeach transmitter.

[0024] The transmitting infrastructure of the invention is unique inthat there is little or no installation cost. The invention utilizesexisting infrastructures (i.e., in-building lighting grids). In mostlocation determining systems, a significant portion of the cost isassociated with the purchase of the infrastructure and its installation.Today, it is not unheard of, for example, to install one RF base stationin every room or at least in every other room in order to providesufficient indoor coverage. The infrastructure for accommodating thesystem and method of the invention, however, can already be found inalmost every office building.

[0025] Converting existing lighting systems to implement the inventioncan be performed by adding a modulation/communications device in serieswith some of the lighting fixtures. Preferably, the device can be partof a light ballast, and conversion can be performed by merely changingthe ballast of some of the lighting fixtures. Ballast manufacturers aredesigning some ballasts to perform a multitude of tasks. For example, itis anticipated that future ballasts will have a unique address similarto an Internet Protocol (“IP”) address. The address could be simply aunique identification code. Alternatively, the address could be a codedform of the relative position of that respective transmitter withrespect to a fixed point. The address could also be the absoluteterrestrial location of that respective transmitter. An example codecould include latitude, longitude, and height relative to sea level.Light ballasts also have dimming capabilities and could include remotecontrol capabilities and optical information transmission features.Thus, ballasts can be modified to include such modulation/communicationsdevices. Alternatively, the modulation device can be added in serieswith an incandescent light bulb fixture. The device can be connected inseries with the light bulb by having both a male and a female light bulbconnection socket. The male connection of the device could be screwedinto the light socket, and then the light bulb can be screwed into thefemale socket of the device. Preferably, each room of a structureincludes at least one of such devices.

[0026] Providing that a relative or absolute location of a given lightsource (transmitter) is known, optical transmission can be applied tocreate a robust indoor location solution. If a receiver is able todetermine the relative location of an optical signal source and theIP-similar address of that source, the receiver can then determines itsown relative or absolute position based on a priori knowledge of thelocation of each transmitter at the structure at issue. Alternatively,the receiver can forward detected/derived information to a centralstation for further processing to determine the receiver's relative orabsolute position.

[0027] The incorporation of the special receivers into the locationsystem of the invention provides a unique method that allows eachreceiver to determine its own relative or absolute location with respectto the rest of the Earth. As a whole, the system of the inventionprovides very accurate indoor and/or outdoor location estimates at afraction of the cost and complexity required by location systemsavailable or known today.

[0028] The construction and method of operation of the presentinvention, however, together with additional objects and advantagesthereof will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings.

[0029] In all the figures of the drawing, sub-features and integralparts that correspond to one another bear the same reference symbol ineach case.

[0030] Referring now to the figures of the drawings in detail and first,particularly to FIG. 1 thereof, there is shown a block diagram of theoverall system architecture of the invention.

[0031] The light bulb 1 represents a single illumination element of amulti-element lighting infrastructure. Preferably, the lightinginfrastructure is located at a building or structure. The system is notlimited to interior or in-building applications. The illuminationelement can be located anywhere on the Earth, whether indoors or not.Preferably, the element is a fluorescent light that is controlled by aballast causing the light to periodically transmit a unique address. Theunique address can be a simple unique identification number.Alternatively, the address can be a code representing a relative orabsolute terrestrial position of the light to which the code isassigned. The address does not necessarily have to be generated andcontrolled by a ballast. The power supplied to the light can be used tovary the illumination such that the light periodically transmits theunique address. Transmission of the address is preferably performed bymodulating the illumination generated by the element into a form that isrecognized as an address signal 2 but is not discernable by the humaneye. Such modulation could include phase modulation, phase shift keying(“PSK”), frequency shift keying (“FSK”), amplitude modulation (“AM”), orfrequency modulation (“FM”). These illustrating examples fortransmitting the address are not to be construed as exhaustive becausevarious equivalent transmitting methods within the knowledge of oneskilled in the art can be used.

[0032] Preferably, the receiver 3 is portable and is built into a watchor similar piece of jewelry, a cellular telephone, or a portable orhand-held computing device such as a laptop computer or a PersonalDigital Assistant (PDA). Alternatively, the receiver 3 can be configuredto reside in a device that is not typically moved. In such aconfiguration, the receiver 3 can be used for security purposes toinsure that the stationary device holding the receiver 3, i.e., acomputer, remains in a particular place.

[0033] The light detector 20 in the receiver 3 can be a conventionaloptical detector, such as a silicon or GaAs detector, a Charged CoupleDevice (“CCD”) detector, and/or a CCD array. As set forth below, theinvention can further include a unique 3-D optical detector thatdetermines its own position relative to a light source.

[0034] As the receiver 3 moves within a building, for example, it passesnear various illumination elements 1 located within the building, manyor all of which are configured to transmit the unique address signal 2.The receiver 3 is preferably configured to show its location on adisplay 4. The display 4 can be attached to the receiver 3 (as shown inFIG. 1). Alternatively, the receiver 3 can transmit location informationto a receiver coupled to a separate display. Such a separate displaycan, for example, show the relative or absolute terrestrial location ofevery remote unit, that is receiver, in a multi-receiver system. In afirst variant, the receiver 3 can determine its distance from orposition relative to illumination elements 1 and forward thatinformation (possibly along with the transmitter address) to anon-illustrated central receiver control station where the relative orabsolute position of the receiver can be calculated with respect to theinfrastructure or to the Earth. Regardless of the configuration, acentral receiver control station could keep track of the currentposition of each receiver.

[0035] If a PDA is used, for example, the PDA display could show in anappropriate screen area the address of the position at which the PDA isbeing held, i.e., a street address. Alternatively, the PDA could show amap identifying the PDA's location with a unique location identifiermarking the spot upon which the PDA is situated, i.e., an “X” on astreet map. Alternatively, the PDA could show a floor plan of thebuilding in which the PDA is being held with a location identifierindicating the position of the PDA. These are not the only examples ofsuch a location display 4. Various equivalent display methods known toone skilled in the art can also be implemented to show the location ofthe receiver.

[0036] Once the receiver 3 detects an appropriate signal 2 from a light,it determines a received signal strength (RSS, also received signalpower) based upon conventional light power detection technologies. Forexample, if the transmission power of the light source is known and thereceiver 3 can determine the received signal power, the receiver 3 canthen determine the two-dimensional distance from that light source basedupon conventional formulas for determining distance based upon theattenuation of the light signal. The receiver 3 simultaneouslydetermines the unique address of the detected illumination element 1 bydemodulating the signal 2 from light received, for example. An examplemethod of demodulation is disclosed in co-pending patent applicationtitled “Interference-Robust Coded-Modulation Scheme for OpticalCommunications and Method for Modulating Illumination for OpticalCommunications,” filed Dec. 8, 2000, as U.S. application Ser. No.09/733,717 and assigned to Motorola, Inc., which is hereby incorporatedherein by reference. Once the address of the detected illuminationelement 1 is obtained, the receiver 3 determines the relative orabsolute position of the illumination element 1 (also called atransmitter) and corrects its own position using the position obtainedfrom the RSS analysis. The corrected position, therefore, pinpoints thereceiver's 3 relative or absolute position in relation to the buildinglayout or to a point on the Earth, for example, within a certain radiusfrom the transmitter 1. The receiver 3 can then display the relative orabsolute position of the receiver 3 to the user or forward thatinformation to a separate display device and/or to a control station.

[0037] The 3-D optical detector 20 of the invention improves theabove-mentioned use of a conventional light detector 20 by generatingmore accurate measurements used to define the exact three-dimensionallocation of the transmitter 1 from the receiver 3. The 3-D opticaldetector 20 will be defined in further detail below.

[0038] In order to detect an appropriate signal, the infrastructure ofthe system must be defined. As set forth above, an existingindoor-lighting infrastructure, for example, is modified so that eachroom or area of a structure includes at least one transmitter 1, each ofwhich having a unique address or identification and transmitting thataddress to the receiver 3. The relative or absolute position of each ofthe transmitters 1 is known.

[0039] In the preferred embodiment, the receiver 3 is connected to alist structure 5. The list structure 5 is a database that holds tworelated pieces of information, a unique address 6 for each lighttransmitter 1 in the infrastructure and a position 7 associated witheach light transmitter 1.

[0040] The list structure 5 is generated at the time systemimplementation begins. Preferably, the list structure 5 is updated toinclude new light transmitters 1 added to the infrastructure, to modifyold light transmitters moved to a new location, or to delete old lighttransmitters removed from the infrastructure. The list structure 5 canreside in the receiver 3 itself, or at a central station where, forexample, the receiver can access the list structure 5 through atransmission link 8. Whether or not the receiver 3 stores the liststructure 5, the list structure 5 is preferably periodically updated.Such an update in the receiver 3 can be done, for example, by modemlinking 8 the receiver 3 to a central computer or station 9 housing themost current version of the list structure 5. The link 8 can be an RFlink, an optical link, and/or an acoustic link. The link 8 can be madethrough an Internet connection (World Wide Web), a direct cellular link,a satellite link, or through the lighting infrastructure itself.

[0041] The list structure 5 update can include replacing the entireupdated list structure 5 in the receiver 3 or saving only changes madeto the list structure 5 since the last update was performed.Accordingly, when a particular light transmitter 1 is detected, thereceiver 3 performs a list/database lookup to determine the relative orabsolute location 7 of that light transmitter 1. Based upon the location7 of that light transmitter 1, the receiver 3 then can begin todetermine its approximate location.

[0042] In the first variant of the present invention, the receiver 3receives and decodes the address of the light transmitter 1 anddetermines the distance from, or position relative to, the lighttransmitter 1 and transmits that information in a position signal to thecentral receiver control station wherein the information is processed todetermine the absolute terrestrial position, or a position relative toanother coordinate system such as a structure.

[0043] In order to determine the exact location of the receiver 3 basedupon light received from an illuminating element 1, a system needs tohave information from which it can extract a three dimensional positionwith respect to that element 1. Most existing location systems need atleast three, and, preferably, four, transmitting devices to calculate atwo-dimensional position. In a preferred embodiment of the invention,the receiver 3 includes a 3-D optical detector 20 that is used tocorrect and enhance the approximate relative or absolute location fromthe corresponding relative or absolute location 7 of the detectedtransmitter 1. The 3-D receiver 20 used by the invention is uniquebecause it determines its own three-dimensional position with the helpof only a single transmitting device 1.

[0044] Shown in block diagram in FIGS. 2 and 4 is a unique SpotCollimating Lens and Charged Couple Device (“SCL-CCD”) structure 20 thatprovides significant features of the 3-D receiver 3. The SCL-CCD 20includes a pinhole lens 22 (shown in cross-section in FIG. 4), a CCDarray coupled to a analog-to-digital (A/D) converter, and a basicprocessor 26. The combination of these elements yields a device thatdetermines the off-axis (θ) and rotational angle-of-arrival (φ) of mostoptical signals. See FIG. 3. The lens 22 is used to collimate a lightsignal 28 into a spot that is detected on the CCD array 24. The CCDarray 24 is a planar matrix of individual photodetector elements, eachof which are mapped to a specific value of θ and φ. When a specificarray element is excited by a column of light 30 that has been filteredfrom the light signal 28, it can be calculated that the column of light30 came from the corresponding angles θ and φ with respect to thereceiver 3. The SCL-CCD 20 also can determine the RSS of the transmitter1 using conventional light power-sensing technologies. The RSS is usedto supplement the SCL-CCD 20 measurements by adding another distancemeasurement.

[0045]FIG. 4 shows a side view of the SCL-CCD 20 in operation in anexample where the incident angle of arrival (θ) of the light 2 is smalland arrives from the right side of the detector 20. If the cross-sectionof the pinhole of the lens 22 in FIG. 4 is extended entirely through theCCD array 24, for example, the view in FIG. 4 is a view of one CCDcolumn 25. Thus, the collimated beam 30 excites an array element 32 onthe left half of the CCD column 25. Preferably, the beam 30 excites asingle element 32 of the column 25. As the angle of incidence (θ)increases, the collimated beam 30 moves toward the center of the CCDcolumn 25. Finally, when the angle of incidence (AoA) is normal to thesurface of the detector (i.e., θ=90°), the collimated beam 30 iscentered on the CCD column 25. Because individual incident angles ofarrival correspond to specific points on the CCD column 25, each elementon the left side of the CCD column 25 is mapped to a particular off-axisangle θ for a light 2 originating on the right side of the CCD column25, for example. The converse algorithm is applied to a light 2 thatarrives from the left side of the CCD column 25.

[0046] The SCL-CCD 20 of the invention, however, involves atwo-dimensional planar CCD array 24. Thus, as a light 2 moves off of theX-axis in either direction of the Z-axis, as shown in FIG. 3, thecollimated beam 30 excites a CCD element 32 that is not located on theX-axis. The angle between the X-axis and a line drawn between the CCDarray 24 center point and the exited CCD element 32 defines a rotationAoA (φ). Thus, the above-mentioned mapping algorithm is extended in twodimensions to map every pixel to each possible off-axis angle (θ) androtational angle-of-arrival (φ). Using the off-axis angle (θ), therotational angle-of-arrival (φ), and the RSS of the optical signal 2, aquite accurate position vector is determined when the orientation of they axis of the SCL-CCD 20 with reference to the coordinate system used todefine the absolute or relative location of the transmitter 7 is eitherpredetermined or determined when the position vector is determined. Forexample, the position of the SCL-CCD 20 can be properly determined whenthe SCL-CCD 20 is known to be oriented vertically while the angles θ andφ are measured. The position vector defines the 3-D position of thereceiver 3 with respect to the source 1 of the optical signal 2.

[0047] The algorithm for mapping the off-axis angle (θ) and therotational angle-of-arrival (φ) to each element of the CCD array canalso be represented by an imaginary rotation of the 2-D off-axis AoA (θ)onto the X-Z plane as shown in FIG. 5. In order to extend the CCDmapping to signals that arrive from anywhere in the 3-D space above thedetector plane 22, the array column on the X-axis is “rotated” so thatit creates a map of concentric circles on the face of the CCD array 24as shown in FIG. 5. The concentric circles enable the measurement of arotational AoA (φ). If the positive X-axis is designated as azero-degree (0°) line for calculating the rotational AoA, a rotationalangle (φ) can be determined for any detectable signal 2 by measuring theangle between a line drawn between the excited element of the array andthe array center point and the positive X-axis. The example shown inFIG. 5 illustrates how four optical signals (each indicated by an “X”)may excite several areas of the detector 20 simultaneously. An area 34of the array 24 including the bottom two X's has been magnified in orderto show how accurate the detector 20 of the invention can be indetermining θ and φ.

[0048] Another set of measurements can be considered. Additionally, oralternatively, the receiver 3 can make TDoA measurements and determineits position based on the time that each signal arrives at its detector20. If, for example, the light signals 2 are transmitted from everyillumination element 1 at the same time, a receiver 3, having a timeclock synchronized with such transmissions, could determine the timethat it took for the received signal 2 to arrive at the receiver 3. Thereceiver 3 then converts the time delay into a distance measurement in aconventional way. The drawback to this alternative technique is arequirement for the transmitters to be synchronized. Althoughsynchronization of transmitters is neither difficult nor expensive, thefeature does increase the complexity of the system.

[0049] The combination of elements 22, 24, 26 in the receiver 20 givesit the capability to detect the 2-D AoA and RSS measurements that arenecessary to determine a 3-D position of a transmitter 1. Anillustration of how the receiver 3 might be used to determine itsposition with respect to multiple light sources 1 in the infrastructuredescribed above and shown in FIG. 1 is taken, for example, from thelighting scenario shown in FIG. 6. The light bulbs represent threeoptical transmitters 40, 42, 44 of an in-building lightinginfrastructure (i.e., fluorescent or incandescent lights), each of whichperiodically transmits a unique address signal 2 within the lightemitted. Once the receiver 3 detects each signal 2, measurements aremade to determine the origin of each signal 2 as set forth above.

[0050] Upon determining its relative location to each light transmitter1 detected by the receiver 3, the receiver 3 displays 4 a highlyaccurate relative or absolute location of the receiver 3 to the user orforwards that information for display on a central display unit and/or acentral control station. Thus, based on a priori knowledge of thelocation of each transmitter 1, a relative or absolute position of thereceiver 3 is determined to a great degree of accuracy.

[0051] The invention has many uses. One example of how the device of theinvention might be used is in concert with the E-911 framework. In theE-911 framework, the system of the invention gives authorities an exactlocation of an emergency (based upon receiving a transmission from areceiver 3 located at that emergency) in a very short time period. Also,the invention can be used by firefighters for locating their ownposition at a structure and/or a position of others at the structure whoare in need of the firefighters' assistance. Further, the invention canbe used by law enforcement for covertly tracking fleeing individualscarrying a receiver of the invention. The invention also can be used forasset tracking. In this embodiment, the receiver is placed on an object(i.e., a computer or a car), and a central location station can monitorthe object as it moves from the detectable range of one transmitter toanother. Alternatively, the invention can be used as a service requestlocator. When an individual desires service personnel (i.e., a waiter),the individual can press an appropriate switch and the service personnelwill be simultaneously notified of the request and the location of theindividual. The invention can be used for providing directions to auser. When a user is lost and needs guidance through streets, forexample, the invention can transmit a position to the system, which, inturn, sends directions back to the user. Finally, the invention can beused for personal security. If a person is in trouble and is in need ofassistance, the invention can be used to transmit the person's locationto an ambulance or to law enforcement for appropriate rescue.

[0052] Although the invention is illustrated and described herein asembodied in an optically-based location system and a method fordetermining a location at a structure, it is nevertheless not intendedto be limited to the details shown because various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

What is claimed is:
 1. A method of determining a location at astructure, which comprises: providing a lighting infrastructure havingtransmitters each optically transmitting a respective relative positionof that transmitter with respect to a fixed position; detecting therespective relative position of at least one of the transmitters with anoptical receiver; and determining a relative position of the receiverfrom the detected relative position.
 2. The method according to claim 1,wherein the transmitters are selected from the group consisting ofultraviolet, infrared, and visible emission devices in the lightinginfrastructure.
 3. The method according to claim 1, which furthercomprises performing the step of determining the relative position ofthe receiver by determining a two-dimensional position of the receiverrelative to at least one of the detected transmitters.
 4. The methodaccording to claim 1, which further comprises performing the step ofdetermining the relative position of the receiver by determining athree-dimensional position of the receiver relative to at least one ofthe detected transmitters.
 5. The method according to claim 1, whichfurther comprises performing the step of determining the relativeposition of the receiver by comparing a received signal strength of atleast one of the detected transmitters with a transmitted signalstrength.
 6. The method according to claim 1, which further comprisessynchronously transmitting the respective relative position of thetransmitters from the transmitters.
 7. The method according to claim 1,which further comprises: calculating a difference between a time atwhich the receiver received a relative position from each of thedetected transmitters and a time at which each of the detectedtransmitters transmitted the relative position to produce a delay time;and converting the delay time into a distance measurement forcalculating a distance between each of the detected transmitters and thereceiver.
 8. The method according to claim 1, which further comprisesperforming the step of determining the relative position of the receiverby transmitting the relative position of the detected transmitters to acentral station and determining the receiver's position with the centralstation.
 9. A method of determining a location at a structure, whichcomprises: providing a lighting infrastructure having transmitters eachoptically transmitting a respective address; providing a list structureassociating each address with a relative position of a respective one ofthe transmitters with respect to a fixed position; detecting at leastone of the transmitters with an optical receiver; determining a positionof the optical receiver relative to at least one of the detectedtransmitters; determining a relative position of at least one of thedetected transmitters from the list structure; and determining arelative position of the receiver from the relative position of at leastone of the detected transmitters.
 10. The method according to claim 9,which further comprises performing the step of determining a relativeposition of at least one of the detected transmitters by: determining anidentity of at least one of the detected transmitters; and selecting acorresponding relative position from the list structure.
 11. The methodaccording to claim 9, which further comprises modulating the opticaltransmission of the respective address in emitted light with thetransmitters and performing the step of determining the relativeposition of at least one of the detected transmitters by demodulatingthe respective address from the emitted light with the receiver.
 12. Themethod according to claim 10, which further comprises modulating theoptical transmission of the respective address in emitted light with thetransmitters and performing the step of determining the identity bydemodulating the respective address from the emitted light with thereceiver.
 13. The method according to claim 9, which comprises opticallytransmitting a respective unique address with each of the transmitters.14. The method according to claim 9, which further comprises providingthe list structure as part of the receiver.
 15. The method according toclaim 9, which further comprises locating the list structure external tothe receiver, and accessing the list structure with the receiver througha transmission link.
 16. The method according to claim 15, which furthercomprises: providing the list structure as part of a central computersystem; and performing the accessing step by accessing the liststructure with the receiver through at least one of the group consistingof a modem, an RF link, an optical link, an acoustic link, an Internetconnection, a direct cellular link, the lighting infrastructure, and asatellite link.
 17. The method according to claim 9, which furthercomprises updating the list structure to include information regardingadditional transmitters added to the infrastructure, to modifyinformation regarding existing transmitters moved to a new position, andto delete information regarding transmitters removed from theinfrastructure.
 18. The method according to claim 9, which furthercomprises performing the step of determining a relative position of atleast one of the detected transmitters by performing a list structurelookup with a processor of the receiver.
 19. The method according toclaim 9, which further comprises performing the two steps of determininga relative position by: forwarding the position of the receiver relativeto the detected transmitters to a central station containing the liststructure; determining a relative position of at least one of thedetected transmitters from the list structure stored in the centralstation; and determining a relative position of the receiver from therelative position of at least one of the detected transmitters with thecentral station.
 20. The method according to claim 19, which furthercomprises transmitting the relative position of the receiver from thecentral station to the receiver.
 21. A method of determining a locationat a structure, which comprises: providing a lighting infrastructure ata structure, the infrastructure having lights and transmitters connectedto the lights for optically transmitting a respective relative positionof that transmitter with respect to a fixed position through emittedlight; detecting the respective relative position of at least one of thetransmitters with an optical receiver; and determining a relativeposition of the receiver from the detected relative position bydetermining at least a two-dimensional position of the receiver relativeto at least one of the detected transmitters.
 22. A method ofdetermining a location at a structure, which comprises: providing alighting infrastructure having lights each optically transmitting arespective unique address through emitted light at a structure definingareas each having at least one of the lights; detecting at least one ofthe lights with an optical receiver connected to a list structureassociating each address with a relative position of a respective one ofthe lights with respect to a fixed position; receiving the respectiveaddress of at least one of the detected lights with the receiver anddetermining an identity of at least one of the detected lights from thelist structure; performing a list structure lookup with a processor ofthe receiver to determine a relative position of at least one of thedetected lights; determining at least a two-dimensional position of thereceiver relative to at least one of the detected lights; anddetermining a relative position of the receiver from the relativeposition of at least one of the detected lights.
 23. A method ofdetermining a location at a structure, which comprises: providing alighting infrastructure having transmitters each optically transmittinga respective address; providing a list structure associating eachaddress with an absolute terrestrial position of a respective one of thetransmitters; detecting at least one of the transmitters with an opticalreceiver; determining a position of the receiver relative to at leastone of the detected transmitters; determining an absolute terrestrialposition of at least one of the detected transmitters from the liststructure; and determining an absolute terrestrial position of thereceiver from the absolute terrestrial position of at least one of thedetected transmitters.
 24. A method of determining a location at astructure, which comprises: providing a lighting infrastructure at astructure, the infrastructure having transmitters connected to lightsoptically transmitting a respective absolute terrestrial position ofthat transmitter through emitted light; detecting the respectiveabsolute terrestrial position of at least one of the transmitters withan optical receiver; and determining a relative position of the receiverfrom the detected absolute terrestrial position by determining at leasta two-dimensional position of the receiver relative to at least one ofthe detected transmitters.
 25. A method of determining a location at astructure, which comprises: providing a lighting infrastructure havinglights each optically transmitting a respective unique address throughemitted light at a structure defining areas each having at least one ofthe lights; detecting at least one of the lights with an opticalreceiver connected to a list structure associating each address with anabsolute terrestrial position of a respective one of the lights;receiving the respective address of at least one of the detected lightswith the receiver and determining an identity of at least one of thedetected lights from the list structure; performing a list structurelookup with a processor of the receiver to determine an absoluteterrestrial position of at least one of the detected lights; determiningat least a two-dimensional position of the receiver relative to at leastone of the detected lights; and determining an absolute terrestrialposition of the receiver from the absolute terrestrial position of atleast one of the detected lights.
 26. A method of determining a locationat a structure, which comprises: providing a lighting infrastructurehaving transmitters each optically transmitting a respective absoluteterrestrial position of that transmitter; detecting the respectiveabsolute terrestrial position of at least one of the transmitters withan optical receiver; and determining a absolute terrestrial position ofthe receiver from the detected absolute terrestrial position.
 27. Anoptically-based location system, comprising: a lighting infrastructurehaving optical transmitters each configured to illuminate and totransmit a respective relative position of said transmitters withrespect to a fixed position; and an optical receiver configured todetect at least one of said transmitters and to determine from thedetection a relative position of said receiver.
 28. The system accordingto claim 27, wherein said lighting infrastructure is inside a structure.29. The system according to claim 27, wherein said transmitters arelights in said lighting infrastructure.
 30. The system according toclaim 27, wherein said lighting infrastructure includes fluorescentlights each with a ballast, and each of said transmitters is part of aballast of said fluorescent lights.
 31. The system according to claim27, wherein said transmitters are configured to transmit said respectiverelative position through emitted light.
 32. The system according toclaim 27, wherein said transmitters are configured to transmit saidrespective relative position through modulation of emitted light andsaid receiver is configured to demodulate said respective relativeposition from the emitted light.
 33. The system according to claim 27,wherein each of said transmitters is a fluorescent light controlled by aunique ballast effecting a periodic transmission of said respectiverelative position through emitted fluorescent light.
 34. The systemaccording to claim 33, wherein said unique ballast is configured tocontrol power supplied to said fluorescent light for varyingillumination into a form recognized by said receiver as said respectiverelative position.
 35. The system according to claim 27, wherein saidunique ballast is configured to modulate illumination from saidfluorescent light into a form recognized by said receiver as saidrespective relative position.
 36. The system according to claim 27,wherein said transmitters have a transmit signal strength and saidreceiver has an optical power detector for detecting a received signalstrength and for comparing said received signal strength to saidtransmit signal strength to form a distance measurement.
 37. The systemaccording to claim 27, wherein said receiver is portable.
 38. The systemaccording to claim 27, wherein said receiver is located in a deviceselected from the group consisting of a piece of jewelry, a cellulartelephone, and a portable computing device.
 39. The system according toclaim 38, wherein said portable computing device is one of the groupconsisting of a laptop computer and a personal digital assistant. 40.The system according to claim 27, including a display connected to saidreceiver for showing a relative position of said receiver.
 41. Thesystem according to claim 27, wherein said receiver has a display forshowing a relative position of said receiver.
 42. The system accordingto claim 27, wherein said receiver has at least one of the groupconsisting of a silicon detector, a GaAs detector, a charged coupledevice detector, and a charged couple device detector array.
 43. Thesystem according to claim 27, wherein said receiver has athree-dimensional optical detector for determining a three-dimensionalposition of said receiver relative to a single one of said transmitters.44. The system according to claim 27, wherein said receiver has athree-dimensional optical detector for determining three-dimensionalpositions of said receiver relative to a plurality of said transmittersthat are transmitting light simultaneously.
 45. The system according toclaim 44, wherein said three-dimensional optical detector is athree-dimensional spot-collimating lens and charged couple deviceoptical detector.
 46. The system according to claim 45, wherein saidthree-dimensional spot collimating lens and charged couple deviceoptical detector has a pin hole lens, a charged couple device array withan analog-to-digital converter, and a processor for determining anoff-axis angle and a rotational angle-of-arrival of a detected opticalsignal, said pin hole lens configured to collimate received light into aspot to be detected by said charged couple device array.
 47. The systemaccording to claim 46, wherein said lens collimates received light intoa spot to be detected by said charged couple device array.
 48. Thesystem according to claim 46, wherein said charged couple device arrayis a planar matrix of individual photodetector elements, and each ofsaid photodetector elements is mapped to a specific off-axis angle androtational angle-of-arrival.
 49. The system according to claim 46,wherein said three-dimensional spot collimating lens and charged coupledevice optical detector determines a received signal strength of atleast one of said transmitters for calculating a distance.
 50. Thesystem according to claim 27, wherein said receiver and saidtransmitters each include a synchronized timer for synchronouslycommunicating said respective relative position.
 51. The systemaccording to claim 27, wherein said receiver has a processor forcalculating a difference between a time at which said receiver receivedsaid respective relative position from each of said transmitters and atime at which said transmitters transmitted said respective relativeposition to produce a delay time, and said processor is configured toconvert said delay time into a distance between each of saidtransmitters and said receiver.
 52. The system according to claim 27,including a central station coupled to said optical receiver, saidcentral station configured to determine a relative position of saidoptical receiver from at least one of said transmitters detected by saidoptical receiver.
 53. The system according to claim 52, wherein saidcentral station is coupled to said optical receiver through at least oneof the group consisting of a modem, an RF link, an optical link, anacoustic link, an Internet connection, a direct cellular link, thelighting infrastructure, and a satellite link.
 54. An optically-basedlocation system, comprising: a lighting infrastructure having opticaltransmitters each configured to illuminate and to transmit a respectiveaddress; a list structure having a table associating each address ofsaid transmitters with a relative position of each respective one ofsaid transmitters with respect to a fixed position; and an opticalreceiver configured to detect at least one of said transmitters and todetermine from a detection a relative position of said receiver.
 55. Thesystem according to claim 54, wherein said receiver has a detector and aprocessor connected to said list structure and to said detector, saidprocessor configured to determine a relative position of said receiverby executing the steps of: detecting at least one of said transmittersand a transmitted respective address of said at least one of saidtransmitters with said receiver; determining a relative position of saidreceiver with respect to said at least one of said transmittersdetected; accessing said list structure with said processor using saidaddresses detected to obtain a relative position of said at least one ofsaid transmitters stored in said list structure; and correcting saidrelative position of said receiver using said relative position of saidat least one of said transmitters to obtain a relative position of saidreceiver.
 56. The system according to claim 54, wherein each of saidtransmitters is a fluorescent light controlled by a unique ballasteffecting a periodic transmission of said address through emittedfluorescent light and said unique ballast controls power supplied tosaid fluorescent light for varying illumination into a form recognizedby said receiver as said unique address.
 57. The system according toclaim 54, wherein said list structure is part of said receiver.
 58. Thesystem according to claim 54, wherein said list structure is external tosaid receiver and said receiver is coupled to said list structurethrough a transmission link.
 59. The system according to claim 58,including a central computer system hosting said list structure, saidtransmission link including at least one of a modem, an RF link, anoptical link, an acoustic link, an Internet connection, a directcellular link, the lighting infrastructure, and a satellite link. 60.The system according to claim 54, wherein said list structure is to beupdated to add information to said table regarding new transmittersadded to said infrastructure, to modify information in said tableregarding existing transmitters moved to a new position in saidinfrastructure, and to delete information in said table regardingtransmitters removed from said infrastructure.
 61. An optically-basedlocation system, comprising: a lighting infrastructure at a structure,said lighting infrastructure having lights each configured to illuminateand to transmit a respective relative position of said lights throughmodulation of emitted light; an optical receiver configured to detect atleast one of said lights, to demodulate the respective relative positionof detected ones of said lights and to determine from the detection arelative position of said receiver, said receiver having athree-dimensional spot collimating lens and charged couple deviceoptical detector for determining a three-dimensional position of saidreceiver relative to at least one of said lights.
 62. An optically-basedlocation system, comprising: a lighting infrastructure at a structurehaving lights each configured to illuminate and to transmit a respectiveaddress through modulation of emitted light; a list structure having atable associating each address of said lights with a relative positionof each respective one of said lights; and an optical receiverconfigured to detect at least one of said lights, to demodulate saidrespective address from the emitted light, and to determine from thedetection a relative position of said receiver, said receiver having adetector and a processor connected to said list structure and to saiddetector, said processor configured to determine a relative position ofsaid receiver by executing the steps of: detecting at least one of saidlights and a transmitted respective address of said at least one of saidlights with said receiver; determining a relative position of saidreceiver with respect to said at least one of said lights detected;accessing said list structure with said processor using a detectedtransmitted respective address to obtain a relative position of said atleast one of said lights stored in said list structure; and correctingsaid relative position of said receiver using said relative position ofsaid at least one of said lights to obtain a relative position of saidreceiver.
 63. An optically-based location system, comprising: a lightinginfrastructure having optical transmitters each configured to illuminateand to transmit a respective absolute terrestrial position of saidtransmitters; an optical receiver configured to detect at least one ofsaid transmitters and to determine from the detection an absoluteterrestrial position of said receiver.
 64. An optically-based locationsystem, comprising: a lighting infrastructure having opticaltransmitters each configured to illuminate and to transmit a respectiveaddress; a list structure having a table associating each address ofsaid transmitters with an absolute terrestrial position of eachrespective one of said transmitters; and an optical receiver configuredto detect at least one of said transmitters and to determine from adetection an absolute terrestrial position of said receiver.
 65. Anoptically-based location system, comprising: a lighting infrastructureat a structure, said lighting infrastructure having lights eachconfigured to illuminate and to transmit a respective absoluteterrestrial position of said lights through modulation of emitted light;an optical receiver configured to detect at least one of said lights, todemodulate the respective absolute terrestrial position of detected onesof said lights and to determine from the detection an absoluteterrestrial position of said receiver, said receiver having athree-dimensional spot collimating lens and charged couple deviceoptical detector for determining a three-dimensional position of saidreceiver relative to at least one of said lights.
 66. An optically-basedlocation system, comprising: a lighting infrastructure at a structurehaving lights each configured to illuminate and to transmit a respectiveaddress through modulation of emitted light; a list structure having atable associating each address of said lights with an absoluteterrestrial position of each respective one of said lights; and anoptical receiver configured to detect at least one of said lights, todemodulate said respective address from the emitted light, and todetermine from the detection an absolute terrestrial position of saidreceiver, said receiver having a detector and a processor connected tosaid list structure and to said detector, said processor configured todetermine an absolute terrestrial position of said receiver by executingthe steps of: detecting at least one of said lights and a transmittedrespective address of said at least one of said lights with saidreceiver; determining a relative position of said receiver with respectto said at least one of said lights detected; accessing said liststructure with said processor using a detected transmitted respectiveaddress to obtain an absolute terrestrial position of said at least oneof said lights stored in said list structure; and correcting saidrelative position of said receiver using said absolute terrestrialposition of said at least one of said lights to obtain an absoluteterrestrial position of said receiver.
 67. An optically-basedin-building location system, comprising: a lighting infrastructurehaving optical transmitters each configured to illuminate and totransmit a respective address signal; and an optical receiver configuredto: decode the respective address of at least one of said transmitters,determine one of a distance and a position relative to said at least onetransmitter from one or more measurements of the address signal, andtransmit a position signal that includes the determined distance orrelative position.
 68. The system according to claim 67, furthercomprising a central receiver control station that receives the positionsignal and determines one of the absolute terrestrial position, or aposition relative to another coordinate system.